Various image compression techniques have been proposed to reduce the amount of data used to represent a digitized color image while, at the same time, providing quality image representation. How much the image is compressed, given in terms of a compression ratio, depends on the image itself, the technique used and the amount of information loss that can be tolerated. Some of these techniques are “lossless,” meaning that they preserve all information of the original image so that it is reproduced exactly when the data is decompressed. Other techniques, commonly referred to as “lossy,” discard information which is visually insignificant. By only approximating the original image rather than reproducing it exactly, lossy techniques are generally able to produce higher compression ratios than lossless techniques. In selecting the appropriate compression technique and compression ratio, the user must consider the particular image to be compressed, the desired image quality as well as transmission time and memory requirements, with the understanding that higher compression ratios lead to lower transmission times and memory requirements but also produce lower quality images.
A typical high quality digitized color image may use 24 bits per pixel (bpp)—8 bits for each of the three basic color components: red (R), green (G) and blue (B) in RGB color space or for each of the three basic luminance-chrominance components: luminance (Y), chrominance (Cb) and chrominance (Cr) in YCbCr color space. To transmit or store such images in the uncompressed state (i.e., in the spatial or pixel domain) is simply too costly in terms of time, memory, and bandwidth requirements. Thus, applications and devices which store or transmit high quality digitized color images typically do so in a compressed format.
Currently, lossless compression techniques for color images provide for compression ratios approaching 2:1, while lossy compression techniques provide for compression ratios approaching 100:1. A lossy compression technique that provides for compression ratios of between 8:1 and 20:1 while maintaining image quality approaching that of lossless compression techniques would therefore be advantageous.